Classifications

• • C—CHEMISTRY; METALLURGY
  • C07—ORGANIC CHEMISTRY
  • C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
  • C07C51/00—Preparation of carboxylic acids or their salts, halides or anhydrides
  • C07C51/41—Preparation of salts of carboxylic acids
  • C07C51/412—Preparation of salts of carboxylic acids by conversion of the acids, their salts, esters or anhydrides with the same carboxylic acid part

Definitions

• the present invention relates to a method of producing solid potassium dipropionate.
• Potassium dipropionate also known as potassium monohydrogen propionate is a complex acid salt containing one mole of propionate ion and one mole of propionic acid per mole of potassium ion.
• Aqueous solutions of potassium dipropionate and the use thereof as a preservative is claimed and described in British Patent Specification No 1505388.
• Solid acid salts are more difficult to prepare because of their inherent instability. For instance sodium dipropionate rapidly loses a mole of propionic acid when exposed to atmosphere leaving the neutral, sodium propionate salt behind. Moreover, the acid salts when produced are not free flowing unless precautions are taken during preparation and storage of the complex acid salts.
• GB 1473447 discloses a method of producing complex acid salts of this type by preparing a fluidised bed of the solid neutral salt and spraying the solid neutral salt in the fluidised bed with the free acid.
• the process is cumbersome because it involves using vapours of the free acid which is relatively corrosive and also possesses an unpleasant odour.
• the present invention is a process for producing solid potassium dipropionate said process comprising mixing an aqueous solution of neutral potassium propionate with an equimolar proportion of propionic acid and cooling the mixture, characterised in that the propionic acid is mixed with the aqueous solution containing at least 85X w/w of the neutral propionate at a temperature above 30°C, the mixture is cooled to a temperature of 30°C or less to enable the solid dipropionate to crystallise and the dipropionate is thereafter recovered.
• the aqueous solution containing more than 85% w/w, preferably from 85 to 90% w/w of the neutral propionate is preferably prepared by dissolving neutral potassium propionate which is free of any water of crystallisation either in water or in a relatively dilute aqueous solution of the neutral propionate.
• the neutral potassium propionate free from water of crystallisation is a desirable starting material because potassium propionate normally crystallises with one mole of water of crystallisation and such crystals are difficult to redissolve in water unless high temperatures are used. Moreover direct evaporation of dilute aqueous solutions of the neutral propionate to produce a concentrated aqueous solution containing more than 85X w/w of the neutral salt is difficult because at about 80% concentration the solution becomes viscous and the neutral salt monohydrate begins to separate which is difficult to redissolve. Moreover, the viscosity of the solution increases sharply thereby making continued stirring and evaporation of the solution difficult. Hence the use of a neutral salt free of water of crystallisation is preferred.
• the neutral salt free from water of crystallisation may be prepared by spray drying an aqueous solution of the neutral salt.
• the relatively dilute aqueous solution used for this purpose suitably has a neutral salt content of less than 85% w/w preferably from 40 to 60X w/w, most preferably from 45 to 55X w/w.
• the neutral salt so produced though slightly moist is substantially free of water of crystallisation and dissolves easily in water.
• the solid neutral salt free of water of crystallisation may be dissolved either as such in water to derive the appropriate concentration or may be mixed with the appropriate amount of a previously prepared relatively dilute aqueous solution of the neutral salt which was used for the spray drying stage.
• the concentrated aqueous solution of the neutral salt so produced and having a neutral salt content of above 85% w/w is then mixed with an equimolar amount of propionic acid at a temperature above 30°C, typically from 55 to 65°C.
• a temperature above 30°C typically from 55 to 65°C.
• the resultant mixture is cooled down to a temperature of 30°C or less, preferably from 20 to 30°C thereby enabling solid, crystalline potassium dipropionate to separate.
• the product dipropionate is thereafter separated and recovered by conventional techniques.
• the product thus produced is a crystalline solid, which is free flowing and is stable.
• the solid potassium dipropionate can be used as a preservative, either alone or admixed with other adjuvants in human foods and in animal feedstuffs.
• Solid crystalline potassium dipropionate was produced as follows:

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• Chemical & Material Sciences (AREA)
• Organic Chemistry (AREA)
• Engineering & Computer Science (AREA)
• Oil, Petroleum & Natural Gas (AREA)
• Organic Low-Molecular-Weight Compounds And Preparation Thereof (AREA)

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Publications (1)

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Cited By (1)

Citations (3)

• 1983
  • 1983-03-26 GB GB838308384A patent/GB8308384D0/en active Pending
• 1984
  • 1984-03-20 EP EP84301865A patent/EP0123416A1/fr not_active Withdrawn
  • 1984-03-22 AU AU26020/84A patent/AU2602084A/en not_active Abandoned
  • 1984-03-26 JP JP5807984A patent/JPS59181236A/ja active Pending

Patent Citations (3)

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